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Publisher: Bristol : IOP × Subject: Semiconductor quantum wells ×

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    Ultrafast two-dimensional terahertz spectroscopy of elementary excitations in solids
    (Bristol : IOP, 2013) Woerner, M.; Kuehn, W.; Bowlan, P.; Reimann, K.; Elsaesser, T.
    Recent experimental progress has allowed for the implementation of nonlinear two-dimensional (2D) terahertz (THz) spectroscopy in the ultrafast time domain. We discuss the principles of this technique based on multiple phase-locked electric field transients interacting in a collinear geometry with a solid and the phase-resolved detection of the THz fields after interaction with the sample. To illustrate the potential of this new method, 2D correlation spectra of coupled intersubband-longitudinal optical phonon excitations in a double quantum well system and a study of ultrafast carrier dynamics in graphene are presented.
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    Dynamics of indirect exciton transport by moving acoustic fields
    (Bristol : IOP, 2014) Violante, A.; Cohen, K.; Lazić, S.; Hey, R.; Rapaport, R.; Santos, P.V.
    We report on the modulation of indirect excitons (IXs) as well as their transport by moving periodic potentials produced by surface acoustic waves (SAWs). The potential modulation induced by the SAW strain modifies both the band gap and the electrostatic field in the quantum wells confining the IXs, leading to changes in their energy. In addition, this potential captures and transports IXs over several hundreds of μm. While the IX packets keep to a great extent their spatial shape during transport by the moving potential, the effective transport velocity is lower than the SAW group velocity and increases with the SAW amplitude. This behavior is attributed to the capture of IXs by traps along the transport path, thereby increasing the IX transit time. The experimental results are well-reproduced by an analytical model for the interaction between trapping centers and IXs during transport.